"The idea of HTML preview would be that it'd be an optional extra step, not something that you get shoved into; eg just like now except with an extra ''preview'' button."

That's what I had in mind. People who could care less about previews would not use it, people who wanted to see the formatting of their post would click the preview button and then click the post button if they were satisfied.

Will second the "meh" and "mer". Why Flash based? Even in 2008 you may not be able to copy and paste the Flash text or have a unique url for a unique post. After a few years even Macromedia's all Flash site blows when it comes to logical navigation (clicking the back button, etc.)